In this demanding service, where tooling is pushed to its limits, a 2-inch router turning at 20,000 r.p.m. will be pushed to feed rates to extract the maximum power available from the spindle, in some instances at feed rates up to 400 inches per minute when using machine spindles capable of 100 HP.
The high metal removal rates and the high centrifugal forces encountered do not in themselves constitute the most rigorous aspect of such high speed milling, which occurs rather on plunging entry into the workpiece by ramping, of which such tools must be capable. That is, the tool must be capable of entering the workpiece by axial penetration of its surface without prior preparation of the workpiece by drilling. This is accomplished by feeding the rotating tool both axially and laterally, either simultaneously or alternately in repetitive steps, procedures which require a cutting capability of each cutting insert in both radial directions, i.e., outward and inward.
The latter cutting action, utilizing the radially inwardly facing cutting edge of the insert, results in a cutting force reaction on the insert whose radial component is outward, acting additively to centrifugal force without benefit of any offsetting inwardly-directed reaction component from the outwardly-facing cutting edge, which is idle in the half-revolution during which the inwardly facing cutting edge cuts.
If the ramping feed is aggressive, the added load upon the insert retainers can be substantial, increasing the danger of separation of the insert from the tool body at high speed.
To the extent the problem has been recognized by the prior art, it has been met by forming the inserts and the insert pockets of the tool body with integral interengageable projections and recesses respectively, in one instance a keel-like projection on the insert receivable in a kerf milled in the seating surface of the pocket. Such measures however are difficult to control in manufacture, and stress the hard metal projections of the insert in a manner that that material is not best suited to withstand.
It is accordingly the object of this invention to provide a simple, easily manufactured, interlocking reinforcement of the attachment of inserts to high-speed, heavy duty routers, to enable them to withstand not only the high centrifugal forces encountered, but also the added force upon the insert retainers resulting from ramping entry into the work.